1. Field of the Invention
The present invention relates to a light source unit, and particularly to a light source unit suitable for use as light sources in business and office machines such as an image scanner, an optical printer, a monochromatic copying machine, a color copying machine, a facsimile machine and the like.
2. Description of the Prior Art
As the light source for business and office machines such as an image scanner, an optical printer, a monochromatic copying machine, a color copying machine, a facsimile machine and the like, desirable are those from which it is possible to obtain an even linear light profile of uniform luminous energy and of no polarization and light which is also irradiation light having a small light distribution beam angle and of substantially parallel rays in order to improve resolution and read rate.
Heretofore, a light source unit wherein a tubular electric lamp of a so-called double-ended type is disposed inside a reflecting mirror has been generally used as one complying with the above described desire for business and office machines such as scanners and the like. The tubular electric lamp is secured at a prescribed position after the focal point is adjusted inside the reflecting mirror.
In the above construction, when the power switch is turned on, the light emitted from the tubular electric lamp is reflected by the reflecting mirror, whereby the light is irradiated on the focal point established at a prescribed position.
In case of degradation failure of a tubular electric lamp as a result of service thereof, the electric lamp is removed from the reflecting mirror, and a fresh tubular electric lamp is again secured at the prescribed position after the focal point is adjusted inside the reflecting mirror.
However, since such a conventional light source, unit utilizes a tubular electric lamp of double-ended type, it is very difficult to obtain an even linear light profile of uniform luminous energy and of no polarization and light which is also irradiation light having a small light distribution beam angle and being composed of substantially parallel rays.
Furthermore, the resulting unit becomes oversized because of employment of such a tubular electric lamp, so that it is difficult to use the unit in a place where there is insufficient space. In addition, since it is required to keep the light transmitting length comparatively long, the design voltage for the electric lamp becomes high. Thus, it is necessary to provide insulating material in order to favorably maintain an insulated condition, and besides there is danger in handling such an electric lamp. Moreover, there is the added disadvantage of requiring a long period of time for exchanging the electric lamp, because the focal point must be adjusted again inside the reflecting mirror at the time when the tubular electric lamp is exchanged.
Still further, a conventional light source unit utilizing a tubular electric lamp exhibits poor irradiation efficiency so that power consumption increases (In general, about 200W-500W), and the resulting irradiation light contains infrared rays so that it results in either thermal degradation of the unit or copying papers, or poor condensing efficiency.
From the practical point of view, it is also very difficult to prepare a light source unit in continuous form from a tubular electric lamp of the double-ended type.